WASHINGTON (Reuters) - Special Counsel Robert Mueller pushed back on Sunday against Paul Manafort's efforts to avoid house arrest, arguing that President Donald Trump's former campaign manager needed to further detail the finances behind his proposed $12 million bail agreement.

In a court memorandum, Mueller and his attorneys argued that the court should only agree to a bail agreement if Manafort fully explains his finances to the court. Prosecutors said his team had not been able to substantiate the value of one of the three properties, as well as several life insurance policies, Manafort wants to pledge for bail.

Manafort, who ran Trump's presidential campaign for several months last year, and associate Richard Gates pleaded not guilty last week to a 12-count indictment by a federal grand jury. They face charges including conspiracy to launder money, conspiracy against the United States and failing to register as foreign agents of Ukraine’s former pro-Russian government.

The two are currently under house arrest, and prosecutors have argued they could pose a flight risk.

The charges are part of Mueller's investigation into alleged Russian efforts to tilt the 2016 election in Trump's favor and potential collusion by Trump associates, allegations that Moscow and the Republican president deny.

In a Saturday court filing, Manafort offered to limit his travel and pledged life insurance worth about $4.5 million as well as about $8 million in real estate assets, including a property on Fifth Avenue in New York that was identified by some media outlets as an apartment in Trump Tower.

But prosecutors said they needed an independent appraisal of that Fifth Avenue property, since Manafort was claiming a fair-market value of the unit that appeared to exceed other outside estimates.

Prosecutors also argued they needed time to talk to Manafort's insurance company about his policies. The prosecutors noted that Manafort would be required to forfeit one of those policies, worth $2.6 million, should he be convicted, creating additional questions about its value in a potential bail agreement.

In the document, Mueller said his team was in talks with Manafort's counsel about striking a bail agreement but that Manafort had not provided enough detail yet on his finances.

"Those discussions are best described as ongoing, and the government is not prepared to consent to a change in the current conditions of release at least until Manafort provides a full accounting of his net worth and the value of the assets that he proposes to pledge," Mueller said in the court memorandum.

U.S. District Judge Amy Berman Jackson said on Thursday that initial bail terms would remain in place and set a bail hearing for Monday to consider changes.